1. Field of the Invention
The present invention relates to a spark ignition engine in which a high RON fuel and a low RON fuel are mixed and supplied to a combustion chamber.
2. Description of the Related Art
The low RON fuel has a good ignition quality and a poor anti-knock quality, and the high RON fuel has a poor ignition quality and a good anti-knock quality. Accordingly, an engine, which is provided with a low RON fuel tank in which low RON fuel is stored and high RON fuel tank in which high RON fuel is stored, and the low RON fuel and the high RON fuel are mixed in accordance with operating conditions of the engine, and the mixture is supplied to a combustion chamber, is known. For example, Japanese Unexamined Patent Publication (Kokai) No. 2001-50070 disclosed such type engine.
In the above type engine, because of providing with two fuel tanks, there is a possibility that low RON fuel and high RON fuel may be improperly stored in the low RON fuel tank and the high RON fuel tank.
For example, a possibility that the low RON fuel may be stored in both the low RON fuel tank and the high RON fuel tank, the high RON fuel may be stored in both the low RON fuel tank and the high RON fuel tank, or the low RON fuel and the high RON fuel may be stored in the high RON fuel tank and the low RON fuel tank, respectively. Consequently, fuel not suitable for an operating condition is injected and the engine performance cannot be fully obtained.
However, the apparatus disclosed in Japanese Unexamined Patent Publication (Kokai) No. 2001-50070 cannot detect the fuel storage failures described above.